This invention relates to vane compressors adapted for use with automotive air conditioning systems, and more particularly to a vane compressor of this kind, which is adapted to obtain sufficient back pressure acting upon the vanes to thereby enhance the degree of contact of the vanes with the camming surface at the start thereof.
Vane compressors are widely employed as refrigerant compressors in air conditioning systems for automotive vehicles by virtue of their structural simplicity and high adaptability to high rotational speed operation. Conventional vane compressors of this kind include a type including a pump housing having an endless inner peripheral camming surface, a rotor having a plurality of slits formed in its outer peripheral surface and a back pressure chamber formed in its interior and communicating with inner ends of the slits, and a rotary shaft drivingly supporting the rotor rigidly fitted thereon, wherein the rotary shaft extends in an airtight manner through a shaft-seal chamber formed in a front head forming part of a compressor casing accommodating the pump housing. In such type compressor, vanes slidably fitted in the slits of the rotor are revolved while in sliding contact with the endless camming surface of the pump housing, to vary the internal volumes of pump working chambers defined by inner surfaces of the pump housing including the camming surface, the outer peripheral surface of the rotor and adjacent vanes for suction and compression of refrigerant gas and discharge of same into a discharge pressure chamber defined between the compressor casing and the pump housing. To ensure achieving required efficiency of suction and compression in such type vane compressor, it is a requisite that the vanes should always be kept in close sliding contact with the camming surface of the pump housing during operation of the compressor. The force for causing close sliding contact of the vanes with the camming surface comprises centrifugal force produced by rotation of the rotor and acting upon the vanes, and internal pressure in the back pressure chamber acting upon the inner ends of the vanes as back pressure. The back pressure is given by compressed refrigerant gas under high pressure flowing from pump working chambers on compression stroke into the back pressure chamber through clearances between the vanes and the slits, clearances between the rotor and vanes and the inner end walls of the pump housing, etc. However, after the compressor has been stopped for a long time, it can often happen that part of the vanes in slits located at an upper half portion of the rotor are receded toward the diametrically center of the rotor with their tips off the inner peripheral camming surface of the pump housing due to their own weights. On the other hand, at or immediately after the start of the compressor, the centrifugal force acting upon the vanes and the pressure of the compressed refrigerant in the pump working chambers are not increased to such levels that the back pressure in the back pressure chamber can urgingly displace the vanes in the radially outward direction into smooth sliding contact with the inner peripheral camming surface of the pump housing, through expansion in the effective internal volume of the back pressure chamber. As a consequence, for some time after the start of the compressor and until the pressure of the compressed refrigerant increases to a required level, the vanes are repeatedly alternately brought into and out of contact with the camming surface to make a percussive noise, often causing damage to the vanes and the pump housing.
Further, in order to lubricate a shaft-sealing portion for sealing the rotary shaft, the compressor of the above described type is constructed such that the shaft-seal chamber accommodating a shaft-seal means is supplied with part of compressed gas with lubricating oil entrained therein from the back pressure chamber through a radial bearing supporting the rotary shaft. However, when the compressor is at rest, the high pressure compressed gas stays in the shaft-seal chamber, causing leakage of refrigerant gas and lubricating oil to the outside of the compressor.
In an attempt to overcome the unsmoothness of radially outward movement of the vanes at the start of the compressor, a compressor has been proposed, e.g. by Japanese Provisional Patent Publication No. 56-107992, in which an inner end face of at least one of the opposite end walls of the pump housing facing cylinder chambers (pump working chambers) is formed therein with two oil grooves communicating with bottom portions of the vane slits forming the back pressure chamber and also communicating with a discharge passage chamber (discharge pressure chamber), respectively, via a communication hole with a restriction provided therein and via a communication hole with a valve provided therein which is adapted to open the hole when the difference in pressure between the discharge passage chamber and the corresponding oil groove is below a predetermined value and to close when the former exceeds the latter, thereby supplying the refrigerant gas from the discharge passage chamber to the bottom portions of the vane slits through the communication holes and the oil grooves to obtain smooth radially outward movement of the vanes at the start of the compressor. However, this proposed compressor has the disadvantages that one of the oil grooves should have a complicated configuiration and the restriction of one of the communication holes should have a very small diameter, thus requiring complicate machining operation.
Besides, the conventional compressors have another disadvantage of poor supply of lubricating oil to radial bearings supporting the rotary shaft at the start of the compressor.